git timetravel to a specific date

git-timetravel.sh

git-timetravel () {

  # If first argument is empty you dun goof'd
  if [ -z "${1}" ]
  then
      echo "Must provide a valid timestamp in roughly ISO 8601"
      echo "Example: git-timetravel "2022-10-01 12:00" main
      exit 1
  fi

  # Guess branch if unset, use currently checked out branch
  if [ -z "${2}" ]
  then
    BRANCH=$(git rev-parse --abbrev-ref HEAD)
    echo "Guessing branch: ${BRANCH}"
  else
    BRANCH=${2}
  fi

  # Via https://stackoverflow.com/questions/6990484/how-to-checkout-in-git-by-date
  # git checkout 'master@{2022-10-01 18:30:00}' is shorter but can go back 90 days max apparently.
  git checkout $(git rev-list -n 1 --first-parent --before="${1}" ${BRANCH})
}